The developments of wireless standards continue to make progress faster than anyone could imagine. FIG. 1 illustrates a timeline of the Wireless Technology Evolution. A first generation (1G) of wireless network communication was provided by analog signals in analog mobile phone systems (AMPS). However, analog mobile phone systems were inefficient in using the bandwidth allocated to the communication channels (i.e., carrier frequencies). As more users desired service at the same time, AMPS became a bottleneck. In the second generation (2G), the wireless communication systems went digital adopting one of a plurality of digital communication standards, such as TDMA, CDMA, or a GSM digital communication standard. Initially, these systems were optimized for voice communication as opposed to data communication. Some wireless communication systems provided limited digital coverage areas as cellular base stations were not installed in every location. Some service providers provided analog roaming in those areas where digital communication was unavailable because the AMPS was universally used in many areas, particularly in the United States. These systems were referred to as dual mode systems. However when communicating in one mode, a user could not switch automatically to another system. That is one could not seamlessly switch from a digital communication system to an analog communication system when the signal faded. Instead, the call was usually dropped and a user would have to redial to use the analog communication system instead of the digital system, which became unavailable for some reason.
In third generation (3G) digital wireless communication systems and protocols, data communication is being emphasized in contrast to voice communication, although voice communication benefits as well from higher bandwidths and data rates. However, to support these new digital wireless communication protocols, the digital cellular infrastructure needs to be updated. That is, the base stations need to be modified to support the new systems. Thus, it will take some time before all base stations support the third generation digital wireless communication system. Thus, a mobile device or unit could move from one location supporting WCDMA, for example, to another location only supporting CDMA. In which case the mobile device or unit needs to be backward compatible with one or more of the older generations of wireless communication systems.
Moreover even if the mobile device or unit is backward compatible, a seamless handoff from one wireless communication system to another during the same communication session was previously unavailable. Presently in order to switch from one communication system to another, a first communication session using the first communication system is manually terminated and a second communication session is manually initiated using the second communication system.
In addition to voice communication, the third generation of digital wireless communication systems has been improved to provide data communication at relatively high speeds.
Referring now to FIG. 2, a chart of parameters for comparing CDMA systems is illustrated. The earlier generation of CDMA system, IS-95, provided a maximum data rate of 9.6 kilobits per second (kbps). The latest generation of CDMA systems, CDMA2000 and W-CDMA, provide a maximum data rate of 384 kbps and 384/2 mega-bits per second (Mbps) respectively to support a High Speed Data Rate (HDR) for data communication.
Referring now to FIG. 3, a chart of parameters for comparing GSM systems is illustrated. Current GSM communication systems provide a maximum data rate of 122 kbps for 8 slots. Third generation of GSM communication systems, EDGE, are being designed to provide a maximum data rate of 553.6 kbps for 8 slots to support a High Speed Data Rate (HDR) for data communication.
As previously discussed, the infrastructure of base stations needs to be upgraded to support the third generation of wireless communication systems. However, the mobile devices or units need to be upgraded as well to support the next generation of wireless communication systems.